Text alignment changed in 2.70
This is a new feature in v2.70. It looks like someone missed to add it to the release notes despite this being a pretty noticeable change.

Proposal / discussion:
https://developer.blender.org/T37761

Commit:
https://developer.blender.org/rBdde5e5ce2581ffd544b442c58d6eefbc1ff61772

AFAIK there is no option to change it other than compiling without this pragma def: USE_NUMBUTS_LR_ALIGN (see above commit).